Hemoglobin E: an emerging hemoglobinopathy in the United States

Unusual pattern in haemoglobin electrophoresis in Croatian population: a case report

Haemoglobinopathies are hereditary disorders of globin chain synthesis and are the most common inherited diseases worldwide. Haemoglobin E is a structural haemoglobin variant characteristic for South East Asian population. We present a rare and unusual finding of haemoglobin E detected in University Hospital Centre Zagreb by capillary zone electrophoresis. Detection of haemoglobin structural variant helped to avoid misdiagnosis of sideropenic anemia and thus potentially harmful therapeutic intervention. In today’s European multiethnic population haemoglobinopathies are a public health issue and Croatian laboratory professionals should be aware of a possibility of finding an unusual haemoglobin pattern.

Hemoglobin E syndromes in Pakistani population

Background

Hemoglobin E is an important hemoglobin variant with a worldwide distribution. A number of hemoglobinopathies have been reported from Pakistan. However a comprehensive description of hemoglobin E syndromes for the country was never made. This study aimed to describe various hemoglobin E disorders based on hematological parameters and chromatography. The sub-aim was to characterize hemoglobin E at molecular level.

Methods

This was a hospital based study conducted prospectively for a period of one year extending from January 1 to December 31, 2008. EDTA blood samples were analyzed for completed blood counts and hemoglobin variants through automated hematology analyzer and Bio-Rad beta thalassaemia short program respectively. Six samples were randomly selected to characterize HbE at molecular level through RFLP-PCR utilizing MnlI restriction enzyme.

Results

During the study period, 11403 chromatograms were analyzed and Hb E was detected in 41 (or 0.36%) samples. Different hemoglobin E syndromes identified were HbEA (n = 20 or 49%), HbE/β-thalassemia (n = 14 or 34%), HbEE (n = 6 or 15%) and HbE/HbS (n = 1 or 2%). Compound heterozygosity for HbE and beta thalassaemia was found to be the most severely affected phenotype. RFLP-PCR utilizing MnlI successfully characterized HbE at molecular level in six randomly selected samples.

Conclusions

Various HbE phenotypes are prevalent in Pakistan with HbEA and HbE/β thalassaemia representing the most common syndromes. Chromatography cannot only successfully identify hemoglobin E but also assist in further characterization into its phenotype including compound heterozygosity. Definitive diagnosis of HbE can easily be achieved through RFLP-PCR.

Hemoglobin e syndromes

Hemoglobin (Hb) E is one of the world's most common and important mutations. It results in a heterogeneous group of disorders whose phenotype range from asymptomatic to severe. Hb E trait and Hb EE are mild disorders. The combination of Hb E and Hb S (Hb SE) results in a sickle cell disease syndrome similar to sickle beta(+) thalassemia. It is important to distinguish Hb E disorders diagnostically because of this marked difference in clinical course among different genotypes. Screening tests, including hemoglobin electrophoresis and high-pressure liquid chromatography (HPLC), may suggest other mutations, unless one is familiar with the findings. E beta-thalassemia, the most serious form of E syndromes, affects a million people worldwide and is increasing in North America. Its phenotype ranges from mild anemia to severe transfusion-dependent thalassemia major. Several genetic modifiers affect the phenotype, including the type of beta-thalassemia mutation, Hb F levels, and co-inheritance of alpha-thalassemia. However, the cause of the phenotypic variability is largely unknown. A prospective natural history study of E beta-thalassemia in Sri Lanka suggests that environmental modifiers are prognostically important. The clinical course of E beta-thalassemia is punctuated by acute and chronic complications that may cause serious morbidity and mortality. Recent studies indicate these patients are at high risk for thromboembolism secondary to a hypercoagulable state increased by splenectomy. Morbidity from iron overload in nontransfused patients secondary to increased gastrointestinal iron absorption is common. Cardiopulmonary disease, including pulmonary hypertension, requires ongoing monitoring and is secondary to iron overload, thromboembolism, and hemolysis-induced nitric oxide deficiency. These patients are excellent candidates for Hb F-modulating agents because moderate changes in hemoglobin may result in marked improvement in phenotype. Recent studies with hydroxyurea indicate 40% of patients will clinically improve with hydroxyurea.

Hematologic problems in immigrants from Southeast Asia

An increasing number of Southeast Asian immigrants have come to North America. Physicians who care for this population should be aware of the high prevalence of hematologic disorders and develop an approach to their diagnosis and management. Malaria and the hematologic sequelae, glucose-6-phophate dehydrogenase deficiency, the thalassemia syndromes, Southeast Asian ovalocytosis, visceral leishmaniasis, HIV infection, and iron-deficiency anemia, all of which may pertain to these patients, are reviewed in this article.

Sickle cell-like crisis and bone marrow necrosis associated with parvovirus B19 infection and heterozygosity for haemoglobins S and E

In the literature, heterozygosity for haemoglobins S and E is known as a clinically benign condition. Nevertheless, we present a case of double heterozygosity manifesting as an infarctive sickle cell-like crisis with acute chest syndrome and reversible bone marrow necrosis. Importantly, these complications were associated with serologically documented parvovirus B19 infection. Reviewing the literature, this case emphasizes a specific role of parvovirus B19 as a precipitating cause. Furthermore, it demonstrates how important the consideration of haemoglobin disorders can be even outside of the historically known areas.

Hematologic disorders in children from southeast Asia

The overall laboratory features of the common RBC disorders occurring in Southeast Asians is summarized in Table 4. These erythrocyte disorders will continue to be important public health issues, and it has been predicted that most new cases of thalassemia in the United States will occur in this population group. The fertility rate in Southeast Asian families is very high, with an average of more than five children delivered by each married woman. This number of children is consistent with perceptions of ideal family size, and, to date, no evidence suggests any change in the size of Southeast Asian families who now reside in the United States. Moreover, attitudes about health care, reasons why one seeks medical attention, and a variety of other cultural issues may impair the effectiveness of genetic counseling and other preventive measures designed to reduce the incidence of serious blood diseases. Genetic screening and prenatal diagnosis clearly have led to a markedly decreased incidence of homozygous thalassemia disorders in high-risk Mediterranean populations throughout the world. With further assimilation into Western culture, a similar disease may occur in the Southeast Asian population also.

Thalassaemic erythrocytes: cellular suicide arising from iron and glutathione-dependent oxidation reactions?

Both beta-thalassaemic red blood cells and normal red blood cells (RBC) artificially loaded with unpaired alpha-haemoglobin chains exhibit increased amounts of membrane-bound haem and iron. In the model beta-thalassaemic RBC the amount of free haem and iron was as much as 20 times that which could have been contributed by the entrapped alpha-haemoglobin chains alone. This excess haem/iron arises from destabilization of haemoglobin via reactions between ferric iron (Fe3+), initially contributed by the unpaired alpha chains, and cytoplasmic constituents, primarily reduced glutathione (GSH). Indeed, in the presence of Fe3+ (100 microM) addition of even small amounts of GSH (0.5 mM) to dilute RBC haemolysates (0.15 mg haemoglobin/dl) greatly accelerated methaemoglobin formation. In contrast, lysates from GSH-depleted RBC demonstrated a significantly reduced rate of iron-mediated haemoglobin oxidation which was reversible by addition of GSH. The initiation, and subsequent propagation, of Fe(3+)-mediated haemoglobin oxidation was significantly inhibited by iron chelators. Finally, Fe(3+)-driven haemoglobin oxidation was synergized by low amounts of H2O2, an oxidant spontaneously generated in thalassaemic RBC. To summarize, the release of small amounts of free iron from unpaired alpha-haemoglobin chains in the beta-thalassaemic RBC can initiate self-amplifying redox reactions which simultaneously deplete cellular reducing potential (e.g. GSH), oxidize additional haemoglobin, and accelerate the red cell destruction.

Heterogeneity of the aggregation response of human platelets to arginine vasopressin

Previous reports have alluded to variability in the aggregation response of normal human platelets to the neuropeptide arginine vasopressin (AVP). Since it has not been well documented, the current studies were undertaken to characterize this response. AVP (1-100 nM) produced a concentration-dependent aggregation response. Although the aggregation response to 100 nM AVP did not correlate with age or sex, there was a bimodal response distribution based on the presence or absence of a second wave of aggregation. In kinetic studies, the apparent km of AVP was 18.3 +/- 5.4 nM. There was a significant inverse relationship between the maximal aggregation response to 100 nM AVP and the km (r = -0.82). One hundred nanomolar AVP increased the intracellular calcium concentration of platelets by 406 +/- 120 nM in calcium free buffer and by 658 +/- 233 nM in the presence of 1.0 mM CaCl2. The aggregation response to 100 nM AVP correlated most strongly with the transmembrane influx of calcium (r = 0.84). In individuals whom 100 nM AVP was able to generate a second wave of aggregation, the selective protein kinase C inhibitor bis-indolylmaleimide significantly decreased the platelet aggregation response. Thus, there is significant heterogeneity in the aggregation response of normal human platelets to AVP. Based on our kinetic studies and the effects of PKC inhibition on the aggregation response to AVP, we would hypothesize that the variability of the aggregation response of normal human platelets to AVP is related to a polymorphism of the platelet AVP V1 receptor.

Screening of antenatal patients in a multiethnic community for beta thalassaemia trait

An investigation of the reliability of screening tests for beta thalassaemia trait in pregnant women was carried out as part of a programme to predict beta thalassaemia major in the fetus. Women with a mean corpuscular volume (MCV) of less than 83fl were examined further, and the reliability of various red cell indices as screening tests was assessed and compared. Over three years 696 women were found to be microcytic and were investigated further. If no abnormal haemoglobin was found by cellulose acetate electrophoresis at alkaline pH, haemoglobin A2 estimation was performed. Beta thalassaemia trait was diagnosed in 56 (8%) of the microcytic women. Both the MCV and the mean corpuscular haemoglobin (MCH) were found to be suitable screening tests for detecting patients who required further investigation. Women found to have beta thalassaemia trait or a functionally equivalent disorder were of varied ethnic origins. Of 58 such women, partners were investigated in 45 instances, and three pregnancies at risk of beta thalassaemia major were identified. Investigations for beta thalassaemia trait should preferably be carried out before pregnancy but for those already pregnant investigation should be carried out, irrespective of whether the patient seems to be iron deficient. It is advisable that partners of women with beta thalassaemia trait have hemoglobin electrophoresis, whatever their red cell indices, as double heterozygosity for either haemoglobin S or haemoglobin E and beta thalassaemia may produce severe disease.